Ystatus is an online tool you can use to check yahoo id's real status. Besides online, offline or invisible status, you are able to see the current avatar (which is downloadable), direct link to chat on ym and direct link to personal profile.
No. Our web tool works independent of the application or platform used by yahoo id's for logging in.
Some of your friends could use Yahoo Messenger, Web Messenger, Email Chat, phone or a third party instant messenger like Meebo, Pidgin, Trillian and other free instant messengers that use the yahoo instant messaging protocol. It's not important what they use, they will be detected for sure.